Garage Supply Help!!!

[Rufat]

Hi everyone.
I am new to this forum. I've just completed my C&G level 2 qualification and started on level 3.
Next week i plan to install a garage supply from the CU in the house to the two way CU in the garage.
I planned everything all wiring diagrams, layout and about to do a product list. The job will be tested by a competent person as soon as i finish it.
But before i start the job i wanted to make sure that everything is correct and need an advice on RCDs in this installation.

It's a TN-S system.
There is an old type metal consumer unit as you can see on the pic.

The supply to the garage CU is by 4mm SWA burried underground and properly terminated at both ends. The earthing will be extended to the garage from the house.

PVC 2 way CU in the garage supplying:
1) Lighting circuit 4x100w bulbs protected by 6A MCB
2)Radial socket circuit supplying 2x double sockets and a fused switch for a 200W pond pump protected by 20A (sockets will be used occasionaly for Power Tools such as hammer drill and circular saw

Cables:
1)1.5mm flat T&E clipped direct for lighting
2)2.5 mm flat T&E clipped direct for Radial

The questions is:
1) Should i add 20 MCB on non RCD side in the main CU and have a 30mA RCD in the garage connected to it?
or
2) supply the garage from existing 60A RCD and have a main switch with 6,20A MCBs in the garage (which will be easier and cost effective)

The outbuilding is only 5m away from the house.

Any advice and information much appreciated.
Regards,
Rufat

 

[guest119]

You say the job will be tested by a competent person, does that mean you dont consider yourself to be so?
How do you plan to gland an armour into a plastic consumer unit?
The existing 60a rcd is just that, an rcd and the 60a is handling current not tripping current.
Therefor if you come straight off this you will only have the main cutout (100a ?) as overcurrent protection.
2 way CU leaves no spare ways.

Boydy

 

[GLENNSPARK]

You say the job will be tested by a competent person, does that mean you dont consider yourself to be so?
How do you plan to gland an armour into a plastic consumer unit?
The existing 60a rcd is just that, an rcd and the 60a is handling current not tripping current.
Therefor if you come straight off this you will only have the main cutout (100a ?) as overcurrent protection.
2 way CU leaves no spare ways.

Boydy

with a gland, banjo n flylead....
why, how do you do it?...with a stuffing gland?...lol..

 

[Octopus]

"Will be tested by a competent person" - oh dear, here we go again. Pop corn anyone?

 

[Rufat]

Hi Boydy,
thanks for reply.
Actually you are right i'm better off with a metal clad CU in the garage (but i think i could run and gland swa to metal adaptable box (close to garage CU) from which i could run the live and eutral (insides of SWA) to the garage CU.
Overcurret protection will be pprovided by MCBs (6A and 20A) in the garage CU. and residual current protection/earth fault by RCD in the main CU that is what i was thinking.
I can do and know how to do insulation resistance and continiuty tests, but as it will be my first installation i just want to make sure there are no mistakes made.

So what would you advise on how protect my installation?

 

[Rufat]

))right as i understand you ve gone through this toppic several times and as i am new to this forum and havent got experience as an electritian i appologise for bringin this matter up.

 

[Rufat]

1) Should i add 20 MCB on non RCD side in the main CU and have a 30mA RCD in the garage connected to it?
or
2) supply the garage from existing 60A RCD and have a main switch with 6,20A MCBs in the garage (which will be easier and cost effective)

if none of above options is OK can you advise me please how to solve this situation.
Thanks

 

[Octopus]

1) Should i add 20 MCB on non RCD side in the main CU and have a 30mA RCD in the garage connected to it?
or
2) supply the garage from existing 60A RCD and have a main switch with 6,20A MCBs in the garage (which will be easier and cost effective)

if none of above options is OK can you advise me please how to solve this situation.
Thanks

Employ a competent electrician?

 

[Thefailsafe2012]

Do you want to be legging it down the garden from your shed to the house to reset the RCD everytime it trips? :angel_smile:

 

[Richard Burns]

1) Should i add 20 MCB on non RCD side in the main CU and have a 30mA RCD in the garage connected to it?
or
2) supply the garage from existing 60A RCD and have a main switch with 6,20A MCBs in the garage (which will be easier and cost effective)

if none of above options is OK can you advise me please how to solve this situation.
Thanks

At least 32A MCB from non RCD side, SWA to 30mA RCD protected CU with appropriate MCBs in garage.
You may find the circular saw inrush current trips a 20A MCB.

 

[Rufat]

Employ a competent electrician?

Ok. How a competent electritian would do it?

 

[Rufat]

At least 32A MCB from non RCD side, SWA to 30mA RCD protected CU with appropriate MCBs in garage.
You may find the circular saw inrush current trips a 20A MCB.

Great. Thats is what i needed. Thank you

 

[Deleted member 72666]

Do you want to be legging it down the garden from your shed to the house to reset the RCD everytime it trips? :angel_smile:

That is a valid argument but how often under normal use is it likely to trip? I've a similar setup and not once has it tripped in 26 years of use! (And yes it has been tested to be okay!)

 

[Rufat]

Do you want to be legging it down the garden from your shed to the house to reset the RCD everytime it trips? :angel_smile:

No of course i dont. Therefore i will follow Richard Burns advise

 

[Thefailsafe2012]

Well just thought it might be a pointer to bear in mind, only based off the fact that a shed is a shed, its outdoors, can be damp, can be home to critters, and probably more likely to trip then a nice warm dry house. That said.....

That is a valid argument but how often under normal use is it likely to trip? I've a similar setup and not once has it tripped in 26 years of use! (And yes it has been tested to be okay!)

You sir must have installed it properly the first time :ihih:

And my brown nosing is done!

Yep I would say Burnsys advise would be the one to take on board mate!

 

[skamuk]

Employ a competent electrician?

Why should he, he's got enough knowledge to do it himself, he just wanted to double check it's all safe. At least he's seeking advice and not just going ahead without being sure. My guess is he can't afford to employ an electrician and seen as he's at college learning this trade, he might as well do it himself and gain some experience. That's what I've been doing as I'm sure you are aware!

 

[skamuk]

Another thing... Aren't you meant to use 4mm on radial circuits, just in case someone comes along and adds more socket outlets? Especially if you end up using a 32a breaker in the garage.

 

[Octopus]

Why should he, he's got enough knowledge to do it himself, he just wanted to double check it's all safe. At least he's seeking advice and not just going ahead without being sure. My guess is he can't afford to employ an electrician and seen as he's at college learning this trade, he might as well do it himself and gain some experience. That's what I've been doing as I'm sure you are aware!

Like you, installing a garden circuit which trips the RCD as soon as you plug something in?

 

[jeremy]

If you have designed the circuit as a radial, and put it's max design current as 20A, then 2.5, under normal conditions, will suffice. If someone wants to change the design to increase it to 32A, that's not your problem. If they add more sockets the cable is protected by the MCB. (How many sockets can you have in a garage!) If the circular saw inrush current looks like it will trip your 20A breaker, use a type C. Hope this helps.

 

[Amp David]

If someone is competent to complete a job, why on earth would they ever log on to an internet forum, where there's more BS flying around than anywhere, to double check they are correct in what they plan.

The last supply I did to a garage was done in bell wire. Its still going strong, saying that though, there are no sockets just a single light BULB

 

[skamuk]

If someone is competent to complete a job, why on earth would they ever log on to an internet forum, where there's more BS flying around than anywhere, to double check they are correct in what they plan.

The last supply I did to a garage was done in bell wire. Its still going strong, saying that though, there are no sockets just a single light BULB

So why are there so many fully qualified registered and experienced sparks on here slating everyone who isn't? Whats the point of them logging in?

A second opinion is better than nothing!

- - - Updated - - -

If you have designed the circuit as a radial, and put it's max design current as 20A, then 2.5, under normal conditions, will suffice. If someone wants to change the design to increase it to 32A, that's not your problem. If they add more sockets the cable is protected by the MCB. (How many sockets can you have in a garage!) If the circular saw inrush current looks like it will trip your 20A breaker, use a type C. Hope this helps.

Understood.

 

[skamuk]

Like you, installing a garden circuit which trips the RCD as soon as you plug something in?

Yea, just like me. The OP could well end up with the same fault and my guess is you will slate him for it. We've got to start somewhere.

 

[Amp David]

So why are there so many fully qualified registered and experienced sparks on here slating everyone who isn't? Whats the point of them logging in?

Didn't know there was.

I'd love to become fully qualified one day, but until then, i'll stick to my methods used day in day out.

 

[Guitarist]

Yea, just like me. The OP could well end up with the same fault and my guess is you will slate him for it. We've got to start somewhere.

Indeed, it's called an apprenticeship.

 

[skamuk]

Indeed, it's called an apprenticeship.

I totally agree, but you don't understand how hard I have tried to get one. If you could help me find one i'd be grateful as I have been searching for over a year now. Even my local council aren't taking on apprentices any more.

 

[Guitarist]

I totally agree, but you don't understand how hard I have tried to get one. If you could help me find one i'd be grateful as I have been searching for over a year now. Even my local council aren't taking on apprentices any more.

I totally understand all the arguments about the lack of availability regarding apprenticeships, but the bottom line is quite simply that if somebody isn't qualified to do something, then they really shouldn't be doing it. Regardless of what I "think" I am capable of, I wouldn't pilot an aircraft simply because "I have tried to get training, but nobody wants to train me", even though I've had a bit of experience.
Getting an apprenticeship has never been easy, regardless of what people think. I myself originally travelled the length of the Country before I got offered a place 180 miles from where I lived at the time. It was while at that centre, that someone there put me in touch with another firm nearer to where I lived. It was extremely difficult to get trained, even back in the 80's and competition was fierce. Unfortunately nowadays, everyone wants everything handing to them with a nice big salary. I missed out on doing lots of things when I was younger, but that doesn't mean it's right for me to have a go now, just because I feel that "the time is right".